The program is concerned with developing animal models for biomedical research utilizing the VRB Genetics Resource by following the appropriate mating techniques. One component of the program involves forming, all on the same genetic background, four groups of mice which are defined with respect to T and B lymphocyte activity utilizing two independently occurring mutations; nude (nu) which results in thymic dysgenesis and a Z-linked mutation which affects the maturation of B lymphocytes. This system is being introduced into 10 inbred mouse strains. Also, the mutant, motheaten (me), is being introduced into four inbred strains of mice and the gene, Dwarf (dw), into three strains. In the rats, the genes Corpulent (cp), Diabetes Insipidus (di), and Jaundice (j) are being introduced into two strains.